<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>css盒模型</title>
    <style media="screen">
        html * {
            margin: 0;
            padding: 0;
        }
    </style>
</head>
<body>
<section class="sec">
    <style media="screen">
        .sec{
            background: red;
        }

        .child {
            height: 100px;
            margin-top: 10px;
            background: yellow;
        }
    </style>
    <article class="child"></article>
</section>
</body>
</html>